1. Field of the Invention
The present invention relates to a liquid ejection apparatus, a cleaning apparatus for a liquid ejection head, and an inkjet recording apparatus, and more particularly to head cleaning technology for wiping a liquid ejection face of a liquid ejection head by means of a long wiping member, and to a liquid ejection apparatus and an inkjet recording apparatus using this technology.
2. Description of the Related Art
In an inkjet recording apparatus, with use, foreign material such as ink residue or paper dust adheres to a liquid ejection face (a nozzle face formed with nozzles) of a liquid ejection head. When the foreign material adheres to the nozzles and/or the periphery thereof, the adhering material affects ink droplets ejected from the nozzles and causes deviation in the ejection direction of the ink droplets, and it is then difficult to deposit the ink droplets at prescribed positions on the recording medium. As a result of this, the output image quality declines. Therefore, in an inkjet recording apparatus, a maintenance operation is carried out to remove foreign material adhering to the nozzle face, periodically or at a suitable timing (see, for example, Japanese Patent Application Publication Nos. 2005-022251 and 2007-030482).
Japanese Patent Application Publication No. 2005-022251 discloses a wiping unit including: a cleaning liquid supply device, which supplies cleaning liquid to a long wiping sheet (wiping member) wound in the form of a roll; and a pressing device, which presses the wiping sheet against the nozzle face of the liquid ejection head. The wiping sheet is paid out from a pay-out reel of a sheet supply unit, and is taken up onto a take-up reel through a pressing roller. By moving the pressing roller over the nozzle face while thus conveying the wiping sheet in a prescribed direction, the wiping sheet is pressed against the nozzle face and caused to rub the nozzle face, thereby wiping the nozzle face. Moreover, Japanese Patent Application Publication No. 2005-022251 proposes to provide the wiping unit with a controller configured to cause a first wiping operation of pressing the wiping sheet impregnated with the cleaning liquid against the nozzle face, and to then cause a second wiping operation of pressing a wiping sheet in a dry state against the nozzle face.
Japanese Patent Application Publication No. 2007-030482 discloses a cleaning apparatus for an inkjet head including: a supporting device, which supports a flexible cleaning device in the form of a sheet, such as a cloth or film, at a position under a lower face of a head; and a pressing device, which presses the cleaning device supported by the supporting device to the lower face of the head from below.
In Japanese Patent Application Publication No. 2005-022251, the pressing roller for pressing the wiping sheet against the nozzle face is constituted of an elastic roller formed by attaching an elastic body of rubber, or the like, to the outer circumference of a shaft (paragraph 0056 in Japanese Patent Application Publication No. 2005-022251). When the elastic roller (pressing roller) moves transversely in the region under the nozzle face, the wiping sheet and the pressing roller are compressed in the downward direction, in such a manner that the wiping sheet is pressed against the nozzle face due to an elastic restoring force of the pressing roller. However, the apparatus according to Japanese Patent Application Publication No. 2005-022251 does not include any device to manage the pressing force.
On the other hand, in Japanese Patent Application Publication No. 2007-030482, the pressing force applied to the head is adjusted by deformation of the pressing device, which deforms elastically upon the pressing action.
However, due to the deformation of the elastic member, the sheet-formed flexible cleaning device (the wiping member such as cloth or film) is distorted, and it becomes impossible to convey the cleaning device. When it becomes impossible to convey the cleaning device due to the occurrence of distortion, the wiping surface of the sheet-shaped cleaning device is not renewed, then the wiping surface having been soiled is used to wipe the head, and hence there is a problem in that the soiling becomes attached again to the nozzle face.
This issue in the related art is described here by a concrete example shown in FIGS. 13 and 14. FIGS. 13 and 14 show a liquid ejection head (hereinafter referred to as the “head”) 520 and a wiping unit 630, which wipes a nozzle face 522 of the head 520. The wiping unit 630 includes: a pay-out side web core 634, which supplies a long wiping web 632; a take-up side web core 636, which takes up the wiping web 632 that has been paid out; a pressing roller 640, which presses the wiping web 632 against the nozzle face 522 of the head 520; an impelling spring 642, which impels the pressing roller 640 and the wiping web 632 wrapped thereon in the upward direction in FIGS. 13 and 14; and a pair of web driving rollers 650, which drives the wiping web 632 to be conveyed.
The wiping web 632 that has been paid out from the pay-out side web core 634 is wound up onto the take-up side web core 636 through a first guide roller 672, a second guide roller 676 and the pressing roller 640. A cleaning liquid deposition roller 662 is disposed between the first guide roller 672 and the second guide roller 676, and is configured to deposit the cleaning liquid on the wiping web 632.
In the composition shown in FIG. 13, a relative movement of the head 520 and the wiping unit 630 is carried out. Here, an example is described where the head 520 is horizontally moved from the left-hand side toward the right-hand side in the direction indicated with an arrow A in FIG. 13, but it is also possible to adopt a composition where the head 520 is stationary and the wiping unit 630 is moved from the right-hand side toward the left-hand side in the drawing.
As shown in FIG. 13, in a state before the wiping web 632 comes in contact with the nozzle face 522 of the head 520, the wiping unit 630 is arranged in such a manner that the uppermost position 638 of the wiping web 632 wrapped around the pressing roller 640 is slightly (for example, by approximately 1.5 mm) higher than the position of the nozzle face 522. When wiping the nozzle face 522, the impelling spring 642 is compressed in accordance with the height differential (the amount of overlap) between the nozzle face 522 and the uppermost position 638 of the wiping web 632, and the wiping web 632 is pressed against the nozzle face 522.
When the wiping web 612 thereby comes in contact with the nozzle face 522 while the impelling spring 622 is compressed, then as shown in FIG. 14, slacks 702 of the wiping web 632 occur on both of the upstream side and the downstream side of the pressing roller 640. For example, if there is the overlap of approximately 1.5 mm, then when the wiping web 632 comes in contact and pressed against the nozzle face 522, the slack 702 of 1.5 mm occurs in the wiping web 632 on each side of the pressing roller 640, i.e., the slacks 702 in total of approximately 3 mm occur on both the sides. In this case, when the web drive roller 650 drives the wiping web 632 at the conveyance speed of 3.2 mm/s, then a state arises in which the wiping web 632 cannot be conveyed for approximately one second between the occurrence and disappearance of the slacks 702. During this time, the nozzle face 522 is wiped with a soiled surface of the wiping web 632.
An issue of this kind is not limited to the inkjet printer, but rather is also a common problem in liquid ejection apparatuses of various kinds which use liquid ejection heads.